1. Field of the Invention
The present invention relates to lighting apparatus using microwave energy, and particularly, to a lighting apparatus using microwave energy capable of improving lighting efficiency.
2. Description of the Background Art
In general, lighting apparatus using microwave energy is a lighting system in which microwave energy generated from a magnetron is transmitted to a resonator through a waveguide, and a fill within a bulb disposed in the resonator emits visible light when excited by the microwave energy. The lighting apparatus using microwave energy has longer life span compared to an incandescent lamp or a fluorescent lamp and has excellent efficiency in lighting.
As shown in FIG. 1, a lighting apparatus using microwave energy comprises a casing 10 having an opening 12 through which microwave energy passes at its one side and a flange 14 outwardly extended from a circumference of the opening 12; a high voltage generator 20 installed inside the casing 10, and for generating and supplying high voltage; a magnetron 30 disposed inside the casing 10, electrically connected with the high voltage generator 20 to generate microwave energy by high voltage; a waveguide 40 fixed to a front surface of the casing 10, and for guiding microwave energy generated from the magnetron 30 toward the opening 12 of the casing 10; a resonator 50 fixed to the flange 14 of the casing 10, communicated with the waveguide 40, and having a resonant region therein where microwave energy is resonated; a bulb 60 rotatably mounted inside the resonator 50, and containing a fill which emits light when excited by microwave energy; a reflector 80 fixed to an outer surface of the casing 10, for forwardly reflecting light emitted from the bulb 60; a fan housing 110 installed inside the casing 10, having an airflow path therein through which an external air is sucked, for cooling heat generated from the high voltage generator 20 and the magnetron 30; a cooling fan 100 provided within the fan housing 110, for sucking external air; a fan motor 101 for rotating the cooling fan 100; a bulb motor 90 for rotating the bulb 60, of which a rotational shaft 92 is connected to a bulb stem 62 extended from the bulb 60; and a disk shaped rear mirror 70 fixed to the flange 14, having a hole 72 at a center thereof in which the bulb stem 62 is inserted.
In the light apparatus according to the conventional art as above, high voltage is generated at the high voltage generator 20 when an external power is applied to the high voltage generator 20, and microwave energy is generated at the magnetron 30 by the high voltage. And, the microwave energy is transmitted to the resonator 50 through the waveguide 40, and excites the fill within the bulb 60. Accordingly, the fill within the bulb 60 emits light, and the reflector 80 reflects the light emitted around the bulb 60. Also, the rear mirror 70 forwardly reflects the light emitted rearwardly from the bulb 60.
At the same time, the cooling fan 100 is rotated by an operation of the fan motor 101, and thus external air out of the casing 10 is sucked into the casing 10 through the airflow path formed inside the fan housing 110. By the airflow inside the casing 10, the high voltage generator, the magnetron 30 and the other internal components are cooled. In addition, the bulb 60 is rotated for being cooled by an operation of the bulb motor 90.
In the lighting apparatus using microwave energy according to the conventional art as above, one of important factors that have an effect on lighting performance is an effective reflection of light emitted from the bulb 60. Accordingly, the reflector 80 is installed around the bulb 60, and the rear mirror 70 is installed at a rear side of the bulb 60, so that the reflector 80 and the rear mirror 70 forwardly reflect light that is emitted around the bulb and to a rear side of the bulb.
However, since the rear mirror 70 provided for the lighting apparatus according to the conventional art is formed in a flat disk shape, the rear mirror 70 cannot effectively reflect light emitted toward the rear of the bulb 60.
Moreover, since the hole 72 is formed in the center of the rear mirror 70 so that the bulb stem 62 is rotatably inserted thereto, even if the hole 72 is formed to have a minimum diameter in which the bulb stem 62 can be rotated in order to reflect the light emitted to the rear of the bulb 60 as much as possible, the light emitted from the bulb 60 is not fully reflected because of the hole 72. Further, the light which is not reflected because of the hole 72 may pass through the hole 72 and may be transmitted to a rear of the mirror 70, or may be scattered by the hole 72, thereby causing degradation in light reflection efficiency
In addition, heat generated from the bulb 60 is transmitted to the bulb stem 62, and thus a thermal damage such that a coated layer is peeled away at a portion adjacent to the bulb stem 62 may be generated. Therefore, components have to be replaced because of such a thermal damage of the rear mirror 70, thereby raising high material and operation costs. In order to prevent the thermal damage, the rear mirror 70 is made of a high priced heat resistible material such as quartz, thereby raising an initial installation cost.